A prospective, controlled study of the effects of hormonal contraception on bone mineral density

OBJECTIVE: To compare the effect of depot medroxyprogesterone acetate (DMPA ) and two types of oral contraceptives (OC) on bone mineral density (BAM) a mong women 18-33 years of age with those not using hormonal contraception. METHODS: Data from 155 women were analyzed. Depot medroxyprogesterone aceta te was administered to 33 women; 63 women who chose oral contraception were randomly assigned to receive either a norethindrone-containing pill (n = 2 8) or a desogestrel-containing pill (n = 35). Fifty-nine women who did not use hormonal contraception served as controls. Lumbar spine BMD was determi ned using dual-energy x-ray absorptiometry at baseline and after 12 months of contraceptive use. We analyzed method-related percent change in BAM whil e controlling for body mass index, calcium intake, exercise, and smoking. W e had approximately 90% power to detect a 2.5% difference between any two g roups. RESULTS: Users of DMPA experienced a mean BMD loss of 2.74% over 12 months compared with controls who sustained a 0.37% loss (P = .01). Users of OCs g enerally demonstrated a gain (2.33% for noretbindrone-containing pills, 0.3 3% for desogestrel-containing pills), which was different from controls amo ng users of norethindrone-containing pills (P = .01), but not among users o f desogestrel-containing pills (P = .99). Observed changes in BMD among DMP A users differed from women who used either type of pill (P < .002). CONCLUSION: Depot medroxyprogesterone acetate has an adverse effect on BMD, in comparison with OCs or nonhormonal methods, when used for 12 months. Re sults must be interpreted cautiously until it is determined whether these e ffects endure or are reversible. (C) 2001 by the American College of Obstet ricians and Gynecologists.